The chimp died Saturday of unknown causes, KING-TV, Seattle, reported.
"Dar signed throughout his life, teaching us about friendships between humans and non-humans and the minds of chimpanzees," said Dr. Mary Lee Jensvold, director of the Chimpanzee and Human Communication Institute at the university. "He will be dearly missed."
Dar was born Aug. 2, 1976, at Holloman Air Force Base near Alamagordo, N.M. During the early years of his life, Dar was raised in a home, treated like a deaf, human child and became the first chimpanzee to learn human sign language.
"Last night I cried my weight in tears over the loss of my friend Dar, but today. more than feeling sad, I just feel grateful," Rozsika Steele, who worked with Dar and other chimpanzees, said in a blog.
An autopsy will be performed in the next few days to determine the cause of death, Jensvold said.